Method of and means for secret signaling



May 8, 1923e VV. E. BEATTY METHOD 0F AND MEANS FOR SECRET SIGNALING Filed Mlgl. 1917 2 Sheets-Sheet l IQOOIO MLM Halli [M7/fam fmffy May 8, 1923. ,454,532 W. E. BETTY METHOD OF' AND MEANS FOR 'SECRET SIGNALING 'Filed Au@ l. '1917 l 2 Sheets-Smet 2 Patented May 8, 1923.

uuiisb sraras 1,454,532 PATENT oFFicE.

WILLIAM E. BEATTY, F BAYSIDE, NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, 0F NEW YORK, N. Y., A. COBCPOBATION- 0F NEW YORK.

METHOD OF ANI) MEANS FOB SECRET SIGNALING.

Application tiled August 1, 1917. Serial No. 183,875.

To all whom it may concern.'

Be it known that I, lViLLiAM E. beam, a citizen of the United States, residing at Bayside, Long Island, in the county of Kings and State of New York, haveinvented certain new and useful Improvements in Methods of and Means for Secret Signaling, of which the following is a full, clear, concise, and exact description.

This invention relates to carrier wave signaling in which messages are transmitted as modulations of a carrier wave. h

An object of the invention is to transmit the modulated carrier wave in such a f orm that it will be unintelligible unless received by specially designed apparatus, `such as disclosed herein.

VVhen-a message in the form of a carrier wave is sent out from a radiating antenna system, this message is liable t o be intercepted by anyone who has a radio receiving system at his disposal. It was early recog nized as being desirable to send a radio message in such a form that it would be umntelligible, or would not be received at all, unless specially designed receiving apparatus were used. Former carrier wave secrecy systems, for the most part, are` open to the objection that the specially vdesigned receiving systems include a motor which must be kept in synchronism with a similar motor at the sending station.

This objection is not applicable the present invention, according to which a method of and means for secret signaling are provided, in which a proper phase relation between the currents at the sending and receiving stations is maintained without the use of synchronously driven moving parts.

In order to get the modulated wave into a form that cannot be handled by ordinary receiving apparatus, advantage is taken of l a previously proposed. scheme, according. to which the unmodulatedcornponents having carrier frequency p may be suppressed, so that a pure modulated 4componenthaving only the side frequencies p-i-a and p-a may be transmitted. In this case a is the instantaneous frequency of the modulating currents. If only the side frequencies p-i-a and p-a are transmitted, this gives an element of secrecy, as this message is unintelligible unless combined at the receiving station with locally generated oscillations of frequency p. In a manner analogous to the production of beats in sound waves, the combination of currents of frequency p with currents of frequency p-i-a for instance, gives the difference frequency a corres onding to the signal which was sent.

ccording to the present invention the unmodulated currents are likewise suppressed, so that only the side frequency p-i-a or p-a or both are transmitted. Instead of keepmg the carrier frequency p constant, however, as previously proposed, the present invention provides for continually chan ing the value of the carrier frequency p, wiile signals are being sent.

If in this case an intercepter attempts to get the message by combining the received waves with the locally generated oscillations of a constant frequency, he will hear in the receiver a4 noise produced by currents having a varying frequency equal to the difference between the frequency of the locally generated oscillations and the frequency of the side band p-l-a or p c, where p is contimially changing. Currents of this character give rise to a siren effect in thereceiver and the signal is not intelligible, The value of the carrier frequency p transmitted is varied rapidly and in an irre lar manner, so that an intercepter wou d be confronted with the problem of similarly varying the frequency of the locally generated oscillations before the received message wave could be rendered intelligible.

The manner in which the present invention provides for varying the locally generated oscillations at the receiving station in the samemanner as the frequency of the carrier oscillations at the sending station, without the use of synchronous motors, will be described in connection with the drawings. in which:

'the station shown in Fig. 1.

In Fig. 1 the oscillation generator 0 of the audion type supplies currents of a frequency which depends on the tuning of the resonant circuit 1. The condenser 2 forms a part of the resonant circuit 1. The condenser 2, as shown in F ig. 2, hasa movable blade 3 which is adapted to be adjustably interleaved with the stationary blade 4:. The movable blade 3 is rotatable through a complete circle and may be given an irregular outline as shown, so that the resonance of the circuit 1 will be varied in an irregular manner as the blade 3 is rotated by the motor 5. The oscillations supplied by the oscillator are hereinafter termed controlc7 oscillations, in order to differentiate them from the carrier oscillations which are modulated in accordance with the signal. Y This scheme of generating variable frequency currents is claimed.

The oscillations supplied by the oscillator 0 may be sent to the amplifier 6 of the audion type and after being amplified are transmitted through the filter 7, which comprises a system of tuned circuits for transmitting the narrow band of frequencies corresponding to the frequency of the control oscillations su plied by the oscillator 0. The

filter 7 and t e other filters shown herein .may be designed in accordance with the showing in the atent to Campbell 1,227,113, May 22, 1917, e ectric lWave filter. The filter 7 is connected to the line 8 and passes only control oscillations, the control oscillations as well as the signal oscillations coming in over line 8 beingsupplied to the input circuit of the modulator M.

The amplifier 6 is coupled, by means of 'transformer 9,'to a harmonic generator 10.

The harmonic generator 10 comprises an -audion which is considerably over-loaded, so that the control oscillations supplied to it are distorted as much as possible, thereby .producing harmonics in the output circuit of this harmonic generator. One of the harmonic frequencies supplied by the generator 10 is used as a carrier wave and the harmonic selected is passed through a band fil -ter l1, amplifier 12, filter 13, similar to 11,

and then by means of transformer 14 to the input circuit of the modulator M. The filters 11 and 13 pass only a band of frequencies corresponding to the carrier frequencies. This modulator comprises tWo audions l5 and 16 connected in opposition and having divided input and divided output circuits. The transformer 14 is connected between the points of division of the input circuits,so that currents supplied by this transformer make both of the audions 15 and 16 of like potential at anyone moment. The signal and control currents supplied by the transformer 17, however, make one of these audions positive when the other is negative. Under this condition the modulator M is the source of a completely modulated wave, this modulator serving to suppress unmodulated currents of the carrier frequency. This modulator forms no part of the present invention and its operation is described fur- Lacasse ther in detail in U. S. Patent No. 1,449,382 to Carson, issued March 27, 1923. The currents supplied by the modulator M may be amplified by any suitable amplifier, such as represented by 18 and then sent to the rad iating antenna 19 or other high frequency line. n this case the radiating antenna 19 supplies carrier oscillations which are modulated in accordance with both the signal; and the control currents. The carrier frequency depends upon the control frequency, and since the latter is continuously changing at a rapid and irregular rate, the frequency of the former is similarly varying.

lin order to translate the modulated Wave sent out from the station in Fig. 1 into an intelligible signal, the a paratus shown at the receiving station in ig. 3 may be provided. The system in Fig. 3 and the use of a control current generator at the sending station as in Fi 1 are described and claimed in British atent No. 131,426. In this ligure the transmitted Wave is received by the antenna 20 which is coupled to a circuit 21, broadly tuned to the band of frequencies to be transmitted. Frequencies selected by the circuit 21 may be amplified by the amplifier 22, transmitted to a tuned circuit 23 similar to 2l, then to detector 24, which may be of the audion type as shown. It has been pointed out that the modulator is a source of a completely modulated wave, the unmodulated currents of the carrier frequency being suppressed. It results that onl the side bands, comprising the sum and di erence frequencies, are transmitted to the receiving station, all as has been pointed out in the above mentioned Carson application. It has further been shown in the -above mentioned patent` that these side bands interact in the detector in such a manner that a component of double modulating frequency (in the present case double control frequency) is included in the output of the tube. The output circuit of detector 24 is coupled by means of transformer 25 to the filter 26, which selectively transmits the currents of the control frequencies. The filter 26 selectively transmits the control oscillations to the power limiting tube and harmonic generator 27, which comprises a threeelement vacuum tube of the audiontype. The potential of the grid 28 of the power tube 27 is maintained positive by means of the battery 29. .The positive charge on the flgrid attracts the electrons emitted by the lament 30 and when the potential supplied to the device 27 reaches a sufficiently high positive value, the electrons will be attracted to the grid to vsuch an extent that no further increase in the current in the plate circuit occurs. The minimum value of the space current in 27 being zero, it is evident that the power delivered by this tube is limited and such limitation is necessary in orderto prevent singing in the circuit comprisin the elements 25, 26, 27, 31, 36 and 37 whic couple the input circuit of the detector 24 to its output circuit. Any other form of power limiting device may, however be used, such for example, as shown in the'latent No. 1,200,796 to Arnold, issued October 10, 1916, in which a resistance limits the current in the output circuit of the thermionic device.

The device 27 operates as a harmonic generator by reason of the fact that it is overloaded, as noted above. This device is similar in type to harmonic generator 10, above described, in that it generates harmonics of the control frequencies supplied to it. In general, waves of the first and second even harmonics would be included in the out-put of said generators. Accordingly, if a second or higher even harmonic of control frequency has been selected from the out ut of tube 10 to determine the carrier requency, locally generated oscillations of the changing carrie-r frequency from tube 27 will be supplied to the amplifier 31. Such a result may readily be accomplished by selectin the second even harmonic from tube 10 to etermine a carrier frequency,to which will correspond the first even harmonic from tube 27. The phase of the amplified locally generated oscillations is properly adjusted by means of the variable inductance 32, variable capacit 33,'and variable resistance 34. Amplifie locally generated oscillations ofthe same phase as that of the carrier frequencies received by antenna 20 are supplied to the resistance 35, which serves as a source of potential for the input circuit of the amplifier 36, the output circuit of which is coupled to the input circuit of detector 24 by means of the transformer 37. Oscillations from the transformer 37 cannot, however, be transmitted through the amplier 22 to the antenna 20, since amplifier 22 is as metrically conducting and only permits the passage of currents in the direction from the antenna to the detector 24.

The wave received by antenna 20 is amplified and detected and the control oscillations are selected bymeans of the filter 26. These control oscillations, of course are varying in frequency in the same manner as the oscillations supplied by the generator 10 at the sending station. The locally generated oscillations of the carrier frequencies supplied by the device 27 after being amplified and adjusted in phase are transferred to the input circuit of detector 24, where the locally generated oscillations combine with the received oscillations to produce currents of the signaling frequency in the out ut circuit of detector 24. Itl has been in icated above that if the sending station transmits a. frequency p-l-a for instance, then at the receiving station locally generatedoscillations of frequency p must be combined with the received wave to reproduce the signal. The signal is reproduced in the same manner here, except that the fre uency of the transmitted waveV and of t e loca 1y generated wave, is continually changing while signaling. The signaling currents may be se ected from the output circuit of detector 24 b means ofthe low frequency filter 38 whic transmits to the line 39 a band of frequencies corresponding to the signaling currents.

While this invention has been described as applicable to signaling, it is apparent that the so-called' signaling currents at the transmitting and receiving stations may be control currents to operate relays or translating devices for any desired purpose.

What is claimed is:

1. The method of wave transmission which. comprises producing a carrier wave, eyclically varying the frequency of said wave, and varying the amplitude of said wave in accordance with a signal.

2. The method of wave transmission which comprises simultaneously modulating a carrier wave, suppressing the unmodulated component, transmitting the modulated carrier wave and continuously varying the carrier frequency.

3. The method of speed transmission which comprises generating a carrier wave, gradually varying the frequenc of said carrier wave and modulating saidvwave in accordance with speech.

4. The method of wave transmission which comprises generating'a carrier wave lqnd simultaneously modulating said wave y va rying its frequency.

5. The method of signaling which comprises generating a carrier wave, modulating said wave in accordance with a signal by varying its amplitude, and in graduall varying the carrier frequency while signa ing. v

6. The method of speech transmission which comprises generating a carrier wave, modulating said wave in accordance with speech, and simultaneously gradually varying the frequency of said wave over a desired range of frequencies.

7. The method of signaling which comprises generating a carrier wave, modulating said Wave in accordance with a signal, suppressing the unmodulated component of said wave, and in varying said carrier frequency while signalin 8. The method o wave transmission which comprises producing and transmitting a wave which has been modulated by vary-l ing its amplitude and continuously varying its frequency.

9. The method of signaling which comprises transmitting a voice modulated Wave ing its amplitude and gradually va and continuously vvarying the carrier `fref quency thereof.

1,0. The method of signaling which -comprises cyclically and continuously varying the frequency ofthe carrier Waves and in ,modulating said Waves by varying their aniplitudes in accordance with a signal.

12. The method ofisignaling which con-y sist-s in supplying control oscillations andv carrier waves, ythe frequency of said carrier waves being dependent on the frequency ofy said control oscillations, modulating said carrier waves in accordance: with a signal and with said oscillations, and in varying the frequency of said control oscillations f whilefsignalsfare beingsent, thereby also varying the frequency of said Waves while signaling.

13. The method vof signaling which comprises cyclicallyvarying the frequency of the; carrier waves, modulating said waves in accordance With a signal, transmitting ythe modulated-waveL and receiving the same at f a distant station, locally generating at said station oscillations whichvr vary in frequency in the same manner as said carrier Waves, and in combining the vreceived modulated wave with the locally generated oscillations f to reproduce the signal. s

14. The method of signaling which comprises supplying control oscillations, chang- 1ing the frequency thereof to provide carrier oscillations, modulating said carrier oscillations in accordance with said control oscillations and with a signal, changing the frequency of said control oscillations While signaling and thereby changing the frequency of said carrier oscillations, transmitting the modulated wave and receiving the same at a distant station, detecting the received Wave thereby produc-ing detected control oscillations, changing the frequency of said detected cont-rol oscillations in the same manner as the frequency of said control oscillations is changed at the sending station to produce locally generated oscillations which vary in frequency as said carrier Waves, and in combining the received Wave with said locally generated oscillation-s to reproduce the signal.

15. The method which comprises generating a Wave of low frequency, obtaining a wave of higher frequency from said Wave of low frequency, modifying said Wave of higher frequency in accordance with said wave of low frequency, and simultaneously varying said Wave of 10W frequency.

16. The method which comprises generating a wave of low frequency, obtaining a wave of higher frequency from said Wave itude of said Waves in aci of low frequency, modifying said wave of higher frequency in accordance with said Wave of'low frequency,'and simultaneously varying the frequency of said wave of low frequency. f f 70 l 17. The method of carrier wave transmisf sion which comprises transmitting a synchronizing impulse as a modulation of a carrier wave having a varyingfrequencyand f maintaining a constant ratio of carrier and impulse frequencies. f

18. A transmission system comprising means for supplying a carrier wave, means for modulatingy saidfwavez'at a frequency which is low as compared with the carrier frequency, and means for gradually varying both of'said frequencies While 'modulating 19. A signaling system comprising means for supplying a carrier Wave, means for modulating said Wave at av frequency ywhich is 10W as compared with the carrier frequency, and mea-ns for gradually varyingy both of said frequencies While signaling.

20. A signaling system comprising means i for supplying an;4 undamped carrier wave, 90y means for modulating said wave by varying its frequency .characteristic in accord ance with a signal, and means forfcyclically varying the frequency of said. wave over a range'of atleast' three frequencies While signaling.

21. A signaling system comprising means for supplying'an undamped carriery wave, having a continuously varying frequency, means for Varying the amplitudel of said 100 Wave in accordance with a signal, and means for transmitting said modulated wave.

22. A signaling system comprising means for supplying an undamped carrier wave having a frequency which varies cyclically over a range of at least three frequencies, and means for modulating said Wave by varying its frequency characteristic in accordance with a signal.

23. In a` signaling system.l the combination of means at a transmitting station forv supplying a carrier wave, said means comprising a resonant circuit, means for cyclically varyingl the resonance frequency of said circuit While signaling, and means for modulating said waves by varying its characteristic in accordance with thesignal.

24. In a signaling system, the combination of means at a transmitting station for supplying a carrier Wave, said means comprising an oscillation generator of the audion type having a resonant circuit, a motor for varying the resonance frequency of said circuit While signals vare being sent, and means for var ing the amplitude of said waves in accor ance with a signal.

25. A signaling system comprising means for supplying carrieroscillations, means for varying the carrier frequency over a range of three or more frequencies, means for 130 lll) sov

'matassa modulating the varying carrier frequency oscillations, and a band filter for transmitting the range of modulated frequencies.

26. .The combination of a sending station comprising means for supplying a carrier wave, means for modulating said wave at a frequency which is low as compared with the carrier frequency, means for c-yclically and continuousl varying the carrier frequency While modu ating, means for suppressing the unmodulated component, and a receiving station comprising means for detecting the received modulated wave.

27. The combination of a sending station comprising means for supplying a carrier Wave, means for modulating said wave in accordance with a signal, means for varying the carrier frequency While signaling, and a receiving station comprising means for supplying locally generated oscillations having the same frequency values and variations as said carrier oscillations, and means for combining the received Wave with the locally geperated oscillations to reproduce the signa y l 28. The combination with means for generating a wave Iof low frequency, of means for obtaining therefrom a wave of higher frequency, means for' modifying'said wave of higher frequency in accordance with said wave of low frequency, and means for varying said low frequency wave while modifying said wave of higher frequency.

29. The combination with means for `generating a Wave of low frequency, of means for obtaining therefrom a Wave of higher frequency, means for modifying said wave of higher frequency in accordance With said Wave of low frequency, and means for varying the frequency of said low frequency wave while modifying said Wave of higher frequency.

30. A radio transmission system comprising a radio sending station, a source of fluctuating current at said sending station, a receiving station adapted to cooperate with said radio sending station, a local source of fluctuating current at said receiving station, and 4common means for simultaneously varying the frequency of both of said sources during transmission.

31. A carrier current transmission system comprising a sending station, a source Yof carrier current at said sending station, a

. receiving station, a local source of iuctuating current at said receiving station, and means for automatically varying the frcquency of said local source an'd the frequency of said carrier current during transmission.

32. A transmission system comprising a sending station, a source of carrier current at said sending station,'a receiving station, a local source of fluctuating current at said receiving station, and means at said sending station for automatically and cyclically varying the frequency of both of said sources during transmission.

33. A radio transmission system comprising means for transmitting a carrier Wave, means for modulating said carrier wave in accordance with synchronizing impulses, and means for simultaneously varying the frequency of the carrier Wave and the frequencv of the synchronizing impulses.

34. The method which comprises transmitting an uninterrupted wave, continuously varying the frequency of said wave and simultaneously modulating said Wave whereby modulations of uninterrupted continuity may be transmitted.

ln Witness whereof, I hereunto subscribe my name this 30th day of July, A. D. 1917.

WILLIAM n. Baa'rrr. 

